Abstract
The purpose of this study was to examine the size of the teeth, dental arch, crowding, and craniofacial morphology in children from nine to ten years of age and the relationship to the timing of the formation of the permanent teeth. We further investigated whether the formation stages of the lower teeth of the subjects with negative overjet develop further ahead than in the case of subjects with positive overjet.
The materials consisted of dental casts, cephalometric X-rays and panoramic X-rays of 94 males and 154 females from nine to ten years of age taken from the files of the Department of Orthodontics, School of Dentistry, Kyushu University. The results were as follows;
1. Tooth formation developed ahead more in females than in males and in the lower teeth more than in the upper teeth. The difference between upper and lower teeth was remarkable in the lateral incisor.
2. The arch width, upper in females and lower in both sexes, was in inverse proportion to tooth formation. Moreover, the arch length was in inverse proportion to the lower tooth formation in males.
3. We were not able to find a significant relationship between the crowding of the mandibular incisors and tooth formation.
4. There was a significant relationship between the craniofacial morphology, such as a steep mandibular plane, posterior rotation of the mandible, long anterior facial height, palatal inclination of the maxillary incisors and large overbite, as well as early developed tooth formation, particularly in males than in females.
5. There was no significant relationship between the size of both jaws and tooth formation.
6. We compared the tooth formation of two groups that were classified according to whether the overjet was positive or negative. The tooth formation, however, did not show significant differences between two groups.
